The present invention relates to superconductors of the high critical temperature ceramic type.
Superconductors are known of the Ba--Ca--Cu--O system such as the ABa.sub.2 Ca.sub.n-1 Cu.sub.n O.sub.x families where n is an integer greater than 1, x is greater than 2n+2, and A is mercury or thallium. Those materials have high critical temperatures, exceeding 100 K for certain phases, i.e. for certain values of n. The critical temperature increases when the material is used at high pressure. For mercury and thallium, it has been observed that the critical temperature increases within a given family with increasing value of n up to n=3, and decreases thereafter.
Those materials are manufactured in the form of ceramics by taking a mixture of precursors in substantially stoichiometric proportion with excess oxygen and subjecting it to high temperatures and pressures.
In spite of the highly advantageous properties represented by compounds of the Hg--Ba--Ca--Cu--O and Tl--Ba--Ca--Cu--O type, research is continuing to find other high critical temperature superconductor ceramics, firstly in the hope of reaching even higher critical temperatures, and secondly for the purpose of avoiding the use of highly toxic substances such as thallium, and to a lesser but non-negligible degree, mercury.